May 14, 2020


The Coronavirus Is Mutating. That's Not Necessarily Good or Bad.: Notions that the novel coronavirus is evolving into a more threatening or benign form prey on our ignorance and fear. (JEREMY DRAGHI & C. BRANDON OGBUNU 05.14.2020, Undark)

For the most part, respected evolutionary biologists have chosen to avoid weighing in on these controversies, opting instead to remain above the fray. This is surprising considering that evolutionary biologists are accustomed to debating creationists, and to the art of public discourse around contentious ideas. Their relative silence leaves a gap that less restrained commenters have rushed to fill: Seemingly every mutation in the novel coronavirus has been spun as a sign that the virus is either adapting to better reproduce and spread in its environment or becoming less harmful.

While genomic differences between different strains of the novel coronavirus are stark facts, our interpretation of those differences can be a wellspring of controversy. And right now, the media coverage of SARS-CoV-2 suggests that the American public fundamentally misunderstands how evolution works -- and how to distinguish between two of its key driving forces, adaptation and genetic drift. The latter represents a gradual accumulation of chance events that have no true consequences for how a virus behaves. And when a particular genetic strain appears to make great leaps in its ability to thrive and proliferate, it's often genetic drift, not adaptation, that's at play.

Researchers at the University of Glasgow drove this point home with a letter and formal critique of the National Science Review study on L and S type viruses. The Glasgow researchers argued that among the study's many technical faults was a fundamental one: The study had failed to test whether the overabundance of the L type could have occurred without changes in the virus' infectiousness. In other words, the researchers had failed to consider a null model -- a model that would have tested whether the patterns they saw in the data could have been caused by random chance.

In casinos, null models give the lie to the notion of "lucky days," showing us that each play is independent of the others: A slot machine is just a machine, and contains about as much magic as the flip of a coin. In science, null models can be used to discipline inferential leaps. They are a reminder that, in most cases, the headline-grabbing explanations are less likely to bear out than the boring ones.

Null models are especially critical for making sense of the mounds of genetic information being collected about SARS-CoV-2 evolution. Evolutionary biologists use the term "genetic drift" to capture the roles of chance and luck in an organism's survival and reproduction, and any good null model must account for these effects of chance. While random, the accumulation of genetic drift across generations can have some surprising consequences; one string of evolutionary luck can cause a biologically insignificant, or neutral, mutation to become predominant in a population. The revelation that most genetic differences among species are neutral was controversial for decades but has now become conventional wisdom. The lesson it offers for the present moment is that most commonly encountered mutations of the novel coronavirus will have absolutely no bearing on the pathogen's ability to infect or sicken humans.

Posted by at May 14, 2020 12:00 AM